1. Field of the Invention
The present invention pertains generally to the field of circuit design and manufacture and, more particularly, to methods for tuning high frequency circuits, such as radio frequency (RF) power amplifier circuits, employing conductive layer strip leads and connectors.
2. Background
In many high frequency circuit applications that require impedance matching, such as RF power amplifier circuits, conventional wire connection technology cannot be used. Instead, conductive metal layers, or xe2x80x9cstrip conductorsxe2x80x9d are used for electrical connection of circuit elements. As used herein, a xe2x80x9cstrip linexe2x80x9d conductor is a conductive layer strip xe2x80x9csandwichedxe2x80x9d between two dielectric layers, whereas a xe2x80x9cmicro stripxe2x80x9d conductor is a conductive layer strip disposed on a dielectric layer and exposed to the environment, i.e., an xe2x80x9copen facedxe2x80x9d sandwich. The use of micro strip and strip line conductors is well known in the art.
In the manufacture of high speed integrated circuit packages, it is often necessary to tune certain component values and circuit performance characteristics after assembly, such as, e.g., transmission or delay times, capacitance, inductance, wavelengths, and/or power losses. Known in the art are various forms of destructive tuning, e.g., laser trimming of resistors. However, destructive tuning can be ineffective, especially where it must be performed before it is known whether a particular circuit element or integrated circuit die will perform as intended.
It is also known in the art that varying the dielectric constant of the dielectric insulating layer(s) in micro strip and strip line conductors affects various electrical properties of the signal being carried thereon. For example, U.S. Pat. No. 5,777,526 to Kawasaki describes a technique of adjusting the transmission delay time per unit length of one strip conductor relative to another by disposing a dielectric layer under the first conductor having a different dielectric constant than a dielectric layer under the second conductor. However, changing a dielectric layer after assembly involves a significant expense, if it is even possible, as it must be removed and replaced on the circuit. Further, any components or conductors attached to the dielectric layer to be removed must also be replaced.
In accordance with one aspect of the invention, a performance characteristic of an electrical circuit employing a strip conductor is achieved by placing a fluid having a selected dielectric property in contact with at least a portion of the strip conductor, such that a dielectric property of the fluid effects one or more transmission characteristics of the conductor. In one embodiment, the performance characteristic is measured, and the dielectric property of the fluid adjusted, respectively, in an iterative process, until the desired performance characteristic of the circuit is achieved.
In preferred embodiments, the strip conductor may comprise either micro strip or strip line type conductors. In one embodiment employing a strip line conductor, one or more portions of an insulating layer are removed from the strip line conductor to expose the conductive strip to the dielectric liquid. In one embodiment, in which a multilayer printed circuit board (PCB) is used as a carrier platform for the circuit, one or more access channels are formed through the PCB layers, proving for contact between the dielectric fluid and portions of a plurality of respective conductors located within the PCB.
Other and further aspects and advantages of the invention will become apparent in view of the following detailed description of the preferred embodiments.